NEW RUKO 16,0 - 30,5 MM TUBE SHEETMETAL DRILL GERMAN MADE HSS DRILLING TOOL BIT,Sketching the quadric surface (KristaKingMath),NIKE AIR MAX 90 GTX ,How to compute invariant manifolds and their reduced dynamics in high-dimensional finite element models | Nonlinear Dynamics,PARTIAL DERIVATIVES] I understand how to get Zx and Zy, but how do you get Zxy? I've attempted several times and I can't figure it out : r/calculus